Monarch butterflies make an amazing 2,500 mile migration from Canada to Mexico every year. It hardly seems possible that such delicate, meandering creatures could propel themselves in any purposeful way for 100 miles in their lifetime, let alone 2,500. Yet this is the well-documented life cycle that monarchs have hewn to since time immemorial.

In recent years, the numbers of monarch butterflies have been declining. The reference indicator for monarch population is how much area they occupy every winter in the forests of Michoacan state in Mexico. In 2013, the butterflies concentrated in just 1.7 acres of territory, which is the lowest on record.

The highest recorded concentration of monarchs was 1996, when they occupied 44 acres.

The good news is that the numbers have been increasing since 2013. This winter, the trees of Michoacan are loaded down with enough butterflies to cover 10 acres, which is an increase of almost four times the population from the year before!

Pinpointing the reason for the resurgence of the species is almost as tricky as explaining what has caused their decline. Deforestation, climate change, pollution, and loss of habitat are all plausible reasons to explain the deterioration of numbers, but what’s so different now that they seem to be coming back? Weather certainly plays a role, and the El Niño effect has translated into butterfly-friendly conditions this year.Butterfly advocate groups such as Monarch Watch believe that their conservation efforts are also contributing to the resurgence, most notably from an initiative to plant milkweed along the migratory routes.

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